As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
The components in an information handling system are conventionally connected together through signal lines, sometimes referred to as traces, that travel along or through a printed circuit board (PCB). For example, an information handling system's motherboard may include thousands of signal lines providing power to and communications between components such as central processing units (CPUs), graphical processing units (GPUs), memory, communication cards, disk drives, and other peripherals. One challenge in PCB design is to maintain the desired characteristic impedance along the entire trace of the signal from one component to another. Interruptions along the trace, including via transitions, discrete resistors and capacitors, and connector leads create discontinuities that negatively affect the signal quality. The problem is exaggerated when the traces are operated at high speeds, such as above 1 GHz. Various techniques have been developed to battle these interruptions, but they all come with drawbacks.
When a high-speed signal like PCIe traverses the PCB, the characteristic impedance is maintained by the proper design of the trace geometry. That is, the width, thickness, curves, heights, and other geometrical characteristics of the trace can be adjusted to obtain a desired impedance. However, when the trace connects to a discrete component, such as a capacitor, a discontinuity occurs. The discontinuity is a result of the capacitance of the soldering pads to allow connection of the discrete component to the traces. An example is shown in FIG. 1, where traces 102A-B and 104A-B are interrupted by connection pads 106A, 106B, 108A, and 108B. The connection pads 106A-B and 108A-B are larger than the underlying traces 102A-B and 104A-B because the connection pads must be visible and accessible to allow installation of the discrete component, such as by soldering the component to the connection pads. This results in the connection pad size being larger than the trace width, which creates a capacitive discontinuity in the pad that effectively reduces the characteristic impedance and creates a signal reflection. When a signal traveling the trace at high-speed encounters the connection pad, some of the signal is transmitted through the connection pad to the component and some of the signal is reflected back from the connection pad.
One conventional technique to reduce the discontinuity resulting from the capacitance is to void a region of the printed circuit board underneath the component. The voiding requires the area of the printed circuit board being voided to be clear of signals on adjacent layers. Recent information handling systems are becoming smaller in size, such as in smaller and thinner laptops and cellular phones, while the systems are offering more features that require more components in the smaller space. Such systems have many traces in a small area for connecting together the components in the small form factor. Voiding part of the PCB in such systems introduces routing challenges for how to be able to fit all the required traces around such voids.
Shortcomings mentioned here are only representative and are included to highlight problems that the inventors have identified with respect to existing information handling systems and sought to improve upon. Aspects of the information handling systems described below may address some or all of the shortcomings as well as others known in the art. Aspects of the improved information handling systems described below may present other benefits than, and be used in other applications than, those described above.